The history of learning and using drills can be traced back to prehistoric times. Stone drills are used by Shuiren Shi for drilling wood to make fire, which is regards as the origin of drills. In modern industry, the twist drills, commonly known as drills, are widely used, which are a hole-machining tool with complicated shape and invented more than a hundred years ago. At present, billions of drills of different types are used across the world. It is reported that the hole-drilling procedure accounts for about a half of the whole making process in America's automobile industry, even higher in aircraft industry. Drilling operation belongs to the field of bore machining, and the hole-making operation is one of the most complicated operations in making process. That's why people have been working on the improvement of drills and drilling procedures.
A head-replaceable carbide modular drill comprises a carbide drill head and a steel tool holder, the head being mounted on the tool holder. For a certain range of hole diameter, the head-replaceable carbide modular drill can fully replace the conventional common-used solid carbide drill. The head-replaceable carbide drill is featured that the drill head can be replaced and the tool holder can be repeatedly used. The consumption of carbide material used for head-replaceable carbide drill heads is far less than that of solid carbide drills, thereby greatly reducing the cost of hole-machining tools.
China patent ZL 200580037359.5 discloses a rotary cutting tool comprising a solid cutter head detachably fixed on a shank portion, the cutter head has a cutting part which is close to the front face of the cutter head and a mounting part which integrates with the cutting part and extends backward from the middle of the cutter head, the shank portion has a receiving part extending from the front face of the shank portion, when the cutter head is fixed to the shank portion, the mounting part is accommodated in the receiving part and the front face of the shank portion protrudes forward and approaches towards the front face of the cutter head.
In an exemplary embodiment of American patent U.S. Pat. No. 7,306,410, the clamping and fixing screw which is screwed in from the circumference of the cylindrical shank extends through the fixing column and the clamping extension portion for clamping the screw in place, the clamping and fixing screw not only provides a definitive fit-connection between the clamping extension portion and the fixing column but also increase the clamping pressure which is applied by clamping extension portion to the frusto-conical surface of the support in the radial direction. In another exemplary embodiment of this patent, the clamping and fixing screw is disposed inside the slot opening in a way that the rotation axis thereof extends along the diameter direction, and the slot opening extends inside the fixing column in the radial direction and is open towards the gradually-tapered end of the fixing column. When the replaceable cutter head is fixed onto the cylindrical shank, extra complexity and longer assembly time are added to the need of the clamping and fixing screw.
American patent U.S. Pat. No. 5,957,631 discloses a rotary cutting tool comprising a cutter head detachably connected to a shank portion, the cutter head and the shank portion are assembled by fitting the shape and size of the circumferential surfaces of the cutter head and the shank portion, a cutting edge is disposed at the front end of the cutter head, the cutter head and the bar portion are advantageously connected by a dovetail-shaped junction configuration to provide firm retention and stable connection, without depending on screws or other connectors. This greatly simplifies the assembly and disassembly of cutter head and shank portion.
The head-replaceable drills in the above patents have cutter head-replaceable function, however, the replacement of cutter head should be implemented by interference fit or screw fastening, in addition, the cutter head and cutter shank have fastening function alone, lacking self-locking function, interference fit fixation leads to strict requirement and big difficulty in manufacture, screw fixation is inconvenient, and both of them lack self-locking fixation function which is simple and easy for assembly/disassembly.